1. Field of the Invention
The present invention relates to an inductively coupled plasma processing apparatus. More particularly, the present invention relates to an inductively coupled antenna having a structure for improving plasma uniformity, and a plasma processing apparatus using the same.
2. Description of the Related Art
Recently, plasma techniques have been widely used in fine processing of substrates during the fabrication of semiconductor devices or flat display panels. In those techniques, plasma is used to etch or deposit predetermined material layers on the surfaces of wafers for fabricating semiconductor devices or on the surfaces of substrates for fabricating liquid crystal displays (LCD). In particular, plasma processing apparatuses have been increasingly used to etch or deposit thin layers on substrates for fabricating highly integrated semiconductor devices.
Examples of plasma processing apparatuses used when fabricating semiconductor devices include capacitive coupled plasma (CCP) processing apparatus, electron cyclotron resonance (ECR) processing apparatuses, helicon processing apparatuses, and inductively coupled plasma (ICP) processing apparatuses. The ICP processing apparatus has advantages of a simplified structure and ease in obtaining plasma of high density and uniformity. Thus, the ICP processing apparatus is most widely used currently.
FIG. 1 illustrates a sectional view of a structure of a conventional ICP processing apparatus. Referring to FIG. 1, a conventional ICP processing apparatus includes a reaction chamber 10 having a plasma forming space therein. An electrostatic chuck 12 for supporting a substrate, for example, a wafer W, is arranged in a lower portion of the reaction chamber 10. A dielectric window 16 is installed in an upper cover 11 of the reaction chamber 10. A gas injection port 14 for injecting a reactant gas into the reaction chamber 10 is formed on a sidewall of the reaction chamber 10. A plurality of gas distribution ports 15, which is connected to the gas injection port 14, is formed in the reaction chamber 10. A vacuum suction port 18 connecting a vacuum pump 19 is formed on a bottom of the reaction chamber 10 for evacuating the inside of the reaction chamber 10 through the vacuum suction port 18. In addition, an antenna 20 for generating plasma in the reaction chamber 10 is installed on the dielectric window 16.
A radio frequency (RF) power supply (not shown) is connected to the antenna 20 to generate RF current through the antenna 20. A magnetic field is created by the RF current that flows through the antenna 20, and an electric field is induced in the reaction chamber 10 by changes in the magnetic field as a function of time. At the same time, the reactant gas is injected into the reaction chamber 10 via the gas distribution ports 15. In this case, electrons excited by the inducted electric field ionize the reactant gas to generate plasma in the reaction chamber 10. The plasma chemically reacts with the surface of the wafer W to perform a desired process, for example, an etching process, on the wafer W. Alternatively, another RF power supply (not shown) is generally connected to the electrostatic chuck 12 in order to supply a bias voltage for increasing the energy of ions that are withdrawn from the plasma and collide against the wafer W.
FIG. 2 illustrates a perspective view of an example of the conventional antenna shown in FIG. 1. As shown in FIG. 2, the general inductively coupled antenna 20 is formed of a conductive coil with a spiral shape.
When the conventional inductively coupled antenna 20 is used, however, the density distribution of the plasma is not uniform in the reaction chamber 10 because the strength of the electric field that is induced by the antenna 20 varies with location. More specifically, the induced electric field is strong at a center portion of the antenna 20 and weak at an edge portion of the antenna 20. Accordingly, the density of the plasma is low at the edge portion of the reaction chamber 10. When the density distribution of the plasma is nonuniform, the depth to which the wafer W is etched or the thickness to which the material layer is deposited on the wafer W is similarly nonuniform. In particular, as a size of the ICP processing apparatus increases, a diameter of the reaction chamber 10 increases, and the uniformity of the plasma density significantly decreases.
As described above, when developing an ICP processing apparatus, it is important to consider the need to maintain a uniform plasma distribution and high-density, as the size of a substrate increases. In addition to the development of a high-density plasma source, the antenna that is the base of an ICP discharge should be designed to improve RF power efficiency and plasma distribution uniformity while reducing damage to the substrate.
However, the above-requirements adversely affect each other. When the RF power is increased, a voltage across the antenna is increased. In addition, in order to maintain high plasma density in a large ICP processing apparatus, the antenna coil should have a large radius and large number of turns. Accordingly, the self-inductance of the antenna is increased so that the voltage across the antenna is increased. When the voltage across the antenna is increased, capacitive coupling easily occurs. Such capacitive coupling excessively increases the kinetic energy of ions, so it is difficult to precisely control the processes. In addition, ions having high kinetic energy strongly collide against the inner walls of the reaction chamber and create particles or collide against the substrate and damage the substrate. Furthermore, when capacitive coupling occurs, RF power efficiency deteriorates.
Accordingly, conventional antennas cannot ensure a uniform distribution of plasma in response to changes in process conditions. In particular, as the size of wafers increases, it becomes more difficult to maintain a uniform distribution of plasma at the edge portion of the wafer using conventional antennas. Accordingly, the quality and yield of semiconductor devices deteriorate.